Conventionally, a technology of conveying substrates such as wafers for manufacturing semiconductors by a robot is used broadly. Here, various processing steps such as a wafer cleaning process, a film-forming process, a heating process, and an etching process are executed when manufacturing semiconductors. The respective processing steps are executed by different processing devices respectively, and therefore wafers need to be conveyed among a plurality of processing devices.
A robot is used for the above-stated wafer conveyance and high cleanliness is required for the surrounding atmosphere in the semiconductor manufacturing process. Therefore, the benefit of an unmanned operation by using a robot is great.
Also, shortening the tact time in conveying wafers is required in order to improve throughput of the semiconductor manufacture. There is a robot conveying a plurality of wafers at the same time by one hand mounted on a robot arm as a technology for shortening the tact time in conveying wafers. A robot of this type holds and takes a plurality of wafers at the same time by one hand from a lot of wafers stored in a FOUP and conveys them to a wafer placing shelf on the processing device side at the same time, for example (Patent Document 1).
Note that there are a process of treating a plurality of wafers at the same time (batch processing step) and a process of treating wafers one by one (single-wafer processing step) in various processing steps in manufacturing semiconductors. When conveying wafers in relation to the batch processing step, the above-stated robot which conveys a plurality of wafers at the same time is suitable.
On the other hand, as the processing step is executed for each wafer when conveying wafers in relation to the single-wafer processing step, conveying processed wafers and un-processed wafers one by one respectively is sometimes advantageous. In this case, the above-stated robot of a system conveying a plurality of wafers at the same time is not suitable.
In Patent Document 2, a substrate holding device including a pair of hands (U-shaped blade members) capable of sagging their interval in the vertical direction is described as a technology of carrying-out one processed substrate and carrying-in one unprocessed substrate at the same time. In this substrate holding device, when a lower hand is in a wafer holding state and an upper hand is in a wafer non-holding state, a vertical interval between the hands is widened. Thereby a wafer held by the lower hand is placed on a lower empty stage of a shelf and the empty upper hand can receive a wafer placed on an upper stage of the shelf at the same time.